As a related-art seat belt apparatus that ensures safety of an occupant of a vehicle, for example, the following seat belt apparatus is known: that is, the seat belt apparatus includes a retractor and an anchor member that are secured to a seat back panel. The retractor retracts and contains a seat belt, and the anchor member guides the seat belt withdrawn from the retractor from a rear side to the front side of a seat back (for example, see Japanese Unexamined Utility Model Registration Application Publication No. 2-105060).
Furthermore, nowadays, a detector referred to as a pretensioner sensor is provided in the retractor. This pretensioner sensor detects a shock or the like in the case of, for example, collision of the vehicle so that the seat belt can be retracted before payout of the seat belt from the retractor is prohibited. This allows the seat belt to restrain the occupant earlier.